Plant Diversity I How Plants Colonized Land Closest relatives??? Green algae called charophyceans are the closest relatives of land plants Why do we think this? Land plants share four key traits only with charophyceans:
Rose-shaped complexes for cellulose synthesis Peroxisome enzymes Structure of flagellated sperm Formation of a phragmoplast NOTE: In charophyceans a layer of a durable polymer called sporopollenin prevents exposed zygotes from drying out LE 29-4 Viridiplantae
Streptophyta Plantae Red algae Chlorophytes Ancestral alga Charophyceans Embryophytes Derived Traits of Plants Five key traits appear in nearly all land plants but are absent in the charophyceans: Apical meristems Alternation of generations
Walled spores produced in sporangia (sporocytes mother cells--go through meiosis to generate spores Multicellular gametangia (archegonia and antheridia) Multicellular dependent embryossome land plants called embryophytes LE 29-5a Apical Meristem of shoot Apical Meristems Developing leaves
Apical meristem Shoot 100 m Root 100 m LE 29-5c Walled Spores Produced in Sporangia Longitudinal section of Sphagnum sporangium (LM) Multicellular
Gametangia Multicellular, Dependent Embryos Archegonium with egg Female gametophyte Spores Embryo Maternal tissue Sporangium 2 m
Sporophyte Gametophyte Male gametophyte 10 m Antheridium with sperm Wall ingrowths Sporophyte and sporangium of Sphagnum (a moss) Archegonia and antheridia of Marchantia (a liverwort)
Placental transfer cell How do we group land plants They can be grouped informally based on presence of VASCULAR TISSUE Bryophytes and Vascular plants LE 29-7 Land plants Vascular plants
Charophyceans Bryophytes Origin of seed plants (about 360 mya) Origin of vascular plants (about 420 mya) Origin of land plants (about 475 mya) Ancestral green alga Grouping non-vascular plants
Bryophytes: 3 phyla (informal names given) Liverworts, phylum Hepatophyta Hornworts, phylum Anthocerophyta Mosses, phylum Bryophyta Which generation is dominant? In all three bryophyte phyla,
gametophytes are larger and longer-living than sporophytes Sporophytes are typically present only part of the time LE 29-8 Raindrop Key Male gametophyte Haploid (n)
Diploid (2n) Sperm Bud Spores develop into threadlike protonemata. A sperm swims through a film of moisture to an archegonium and fertilizes the egg. Antheridia Protonemata
The haploid protonemata produce buds that grow into gametophytes. Most mosses have separate male and female gametophytes, with antheridia and archegonia, respectively. Bud Egg Gametophore Spores Female
Archegonia gametophyte Meiosis occurs and haploid spores develop in the sporangium of the sporophyte. When the sporangium lid pops off, the peristome teeth regulate gradual release of the spores. Peristome The sporophyte grows a long stalk, or seta, that emerges from the archegonium. Sporangium MEIOSIS Mature
sporophyte Capsule with peristome (SEM) Female gametophytes Attached by its foot, the sporophyte remains nutritionally dependent on the gametophyte. The diploid zygote develops into a sporophyte embryo within the archegonium.
More about Bryophyte gametophytes (dominant stage) Bryophyte gametophytes Produce flagellated sperm in antheridia Produce ova in archegonia Generally form ground-hugging carpets and are at most only a few cells thick Bryophyte sporophytes Bryophyte Grow sporophytes
out of archegonia Consist of a foot, a seta, and a sporangium LE 29-9a Gametophore of female gametophyte 500 m Foot Seta Sporangium Marchantia polymorpha, a thalloid liverwort
Marchantia sporophyte (LM) LE 29-9c An Anthroceros hornwort species Sporophyte Gametophyte LE 29-9d Polytrichum commune, hairy cap moss
Sporophyte Gametophyte Ecological and Economic Importance of Mosses Sphagnum, or peat moss, forms extensive deposits of partially decayed organic material known as peat Sphagnum plays an important role in the Earths carbon cycle NOWVascular Plants
(but they are seedless) There are two phyla of seedless vascular plants: Lycophyta includes club mosses, spike mosses, and quillworts Pterophyta includes ferns, horsetails, and whisk ferns and their relatives How are they different than Bryophytes? Sporophyte is the dominant generation The gametophytes are tiny
plants that grow on or below the soil surface Angiosperms Gymnosperms Seedless vascular plants Bryophytes (nonvascular plant) Charophyceans LE 29-UN583
Vascular plants have two types of vascular tissue: xylem and phloem Xylem conducts most of the water and minerals and includes dead cells called tracheids Phloem consists of living cells and distributes sugars, amino acids, and other organic products LE 29-12 Key Haploid (n) Diploid (2n) Spore
New sporophyte Zygote Sorus Gametophyte Fiddlehead FERTILIZATION They have leaves Increase the surface area of vascular plants, thereby capturing more solar
energy that is used for photosynthesis Leaves are categorized by two types: Microphylls, leaves with a single vein Megaphylls, leaves with a highly branched vascular system According to one model of evolution, microphylls evolved first, as outgrowths of stems LE 29-13
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